Wireless Power Transfer for Medical Devices Using Virtual Resistance
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Solution Overview
Problem
Inductive wireless power transfer systems for medical devices face inefficiencies and thermal heating due to varying charging distances, leading to inconsistent battery charging and reduced device lifespan.
Innovation Solution
A wireless power transfer system with a virtual resistance unit in the supply line, connected between a DC-DC buck/boost converter and a transmit amplifier, allows for fine control of transfer conditions, maintaining a constant current and reducing thermal heating by adjusting resistance characteristics based on charging distance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If inductive wireless power transfer is used with varying charging distance, then power transfer capability is provided, but current variation increases by more than a factor of 2 or 3
Solution Approach 1:
The patent applies dynamics by making the virtual resistance tunable and adjustable during operation. The virtual resistance is not fixed but can be dynamically modified based on the charging distance and load conditions, allowing the system to adapt to varying implant depths while maintaining consistent current delivery to the IPG battery.
Solution Approach 2:
The patent changes the resistance parameter in the supply line to compensate for distance variations. By adjusting the virtual resistance value, the system optimizes power transfer efficiency and maintains stable current delivery despite changes in coupling between transmitter and receiver coils over different charging distances.
2Adaptability or versatility
If inductive wireless power transfer is used with varying charging distance, then power transfer capability is provided, but thermal heating increases due to increased average dissipation
Solution Approach 1:
The patent modifies the resistance parameter dynamically to minimize power dissipation and thermal heating. By optimizing the virtual resistance value according to the actual charging distance, the system reduces I²R losses in the supply line and improves overall power transfer efficiency, thereby reducing thermal heating in both the charger and IPG.
Solution Approach 2:
The patent converts the potentially harmful effect of varying distance into a beneficial control mechanism. By introducing a tunable virtual resistance that can be adjusted based on distance, the system transforms the distance variation problem into an opportunity for optimized power transfer, where the resistance adjustment compensates for coupling changes and maintains efficient operation across different implant depths.
3Loss of energy
If inductive wireless power transfer link is designed for fixed distance range, then efficiency is maintained, but adaptability to varying implant depths is reduced
Solution Approach 1:
The patent applies dynamics by implementing a tunable virtual resistance that can be adjusted in real-time based on the charging distance. This dynamic adjustment allows the system to maintain optimal power transfer efficiency across a wide range of implant depths, rather than being constrained to a fixed distance range.
Solution Approach 2:
The patent makes the power transfer system universal by enabling it to operate efficiently across multiple implant depth scenarios. The tunable virtual resistance allows the same system to adapt to different patient anatomies and implant positions, providing consistent performance whether the implant is at 10mm, 20mm, or other depths.
4Reliability
If virtual resistance unit is added to control current, then current consistency is improved, but device complexity increases
Solution Approach 1:
The patent introduces a virtual resistance unit as an intermediary element in the supply line between the DC-DC converter and the transmitter coil. This intermediary component provides current consistency by compensating for load variations, and can be implemented using existing circuit techniques such as digital-to-analog converters and operational amplifiers, minimizing the increase in overall device complexity.
Solution Approach 2:
The patent replaces potential mechanical adjustment mechanisms with electronic control. Instead of physically changing components or mechanical switches, the virtual resistance is controlled electronically through digital signals from the microcontroller, allowing precise current regulation without adding complex mechanical structures.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system provides consistent and efficient power transfer over a wider range of implant depths, minimizing thermal heating and extending battery life by maintaining a constant charging current, even at varying distances between transmitter and receiver coils.
Implementation Method 1
The transmitter antenna and the receiver antenna may be configured to provide a wireless power transfer link
Implementation Method 2
Parallel resonant inductive wireless power transfer systems for medical implant applications
Data Source
AI summary
Inductive wireless power transfer systems are provided for medical devices, such as implantable medical devices (IMDs). The systems may comprise a transmitter unit and a receiver unit and may be configured for transferring power and/or signals from the transmitter unit to the receiver unit and/or vice versa. The transmitter unit may comprise an energy source, a transmitter antenna, and a supply line connected in between the energy source and the antenna. The receiver unit may comprise a receiver antenna and a rectifier output. The transmitter antenna and the receiver antenna may be configured to provide a wireless power transfer link. The supply line may comprise a virtual resistance unit, which may be configured to provide a virtual resistance, which may be determined such that the rectifier output provides a substantially constant or less varying charge current over a predetermined distance range, for a large range of implant depths.